We lyophilized 50mg/ml mAb with PI of 7.5 in a 10mM His buffer pH 6.2. Upon reconstitution the pH is 6.5. Does anyone have an explanation for this? I am under the impression His is much less susceptible to pH change during lyophilization as opposed to something like a phosphate buffer. Thanks.
Yes! Freezing forces the solutes out of solution, the pH changes can be considerable! There is a good webinar on this by Kevin Ward under the heading of Freeze Drying Diagnostic Reagents - see https://www.spscientific.com/Webinars/Archives/ also the recent webinar on Phase Transformations (top of the list) may apply. I remember Dr Henning Giesler saying the phosphate buffer was one of the worst for this. The issue is what happens to the buffer components when you freeze, also the sample. There is some talk abot the size of the ice crystals (i.e. ice suface area) having an effect on protein aggregation - that's a Dr John Carpenter area of expertise, at Colorado.
kind regards
Rob
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